1. Field
Exemplary embodiments relate to a navigation system, and more particularly, to a global positioning system (hereinafter, referred to as GPS) receiver and a satellite clock correcting method thereof.
2. Description of Related Art
A GPS, in general, is a system developed to determine a location of an object. A GPS service enables a user to determine his location by receiving GPS signals from GPS satellites, measuring information related to a current location of the user, and providing the measured information to the user.
In addition, the GPS service is utilized as a navigation service using data such as map information, traffic information, and the like. When a user selects a destination, navigation information, such as traffic information from a current location to the destination or direction information is provided to the user using previously stored map information. Further, a GPS service can be applied to various fields related to positioning, military, aeronautical operational controlling, and the like. Thus, it is possible to acquire location and time information using the GPS service.
A GPS comprises at least one GPS satellite that broadcasts a GPS signal in space and a GPS receiver that provides location information in response to the GPS signal.
A GPS typically includes twenty-four GPS satellites, in practice, twenty-seven GPS satellites including three supplement satellites, having different orbits. This enables the GPS receiver to acquire GPS signals from four or more GPS satellites. Herein, the GPS receiver has to establish contact with or secure four or more GPS satellites in order to acquire four or more GPS signals. The GPS receiver can calculate a pseudo-range, or an approximation of the distance between the GPS satellite and the GPS receiver, in order to acquire location information. For example, the GPS receiver can calculate the pseudo-range by measuring a difference between a time when the GPS satellite broadcasts a satellite signal and a time when the GPS receiver receives the satellite signal.
It is possible to acquire location information based on whether a GPS time stored in a GPS receiver, that is, time derived from a satellite clock, is exact. The GPS receiver can determine a satellite clock using information included in a GPS signal provided by the GPS satellite. A GPS satellite orbits about the earth, and does not remain at a fixed location. However, in cases where information included in a GPS signal can be employed when measuring a satellite clock, satellite circumstance information pertaining to the orbit of a GPS satellite, for example, satellite velocity and location information, is not considered when measuring of a satellite clock. Therefore, it is difficult to measure a satellite clock accurately. Accordingly, errors may occur when determining a location.